This invention relates generally to a method and apparatus for guiding the passage of a moving elastomer-jacketed cable from one vertical path, through 180.degree., to another vertical path. More particularly, the invention relates to a method and apparatus for use at the top of a high elevation lighting pole for guiding a moving power cable through 180.degree. from its path within the interior of the pole to the exterior of the pole where the cable connects with a cluster of luminaires which are lowered from the pole top to the base of the pole for servicing.
It is a practice in the high-mount lighting industry to employ self-contained raise/lower devices to bring luminaires down to the ground for maintenance instead of using bucket trucks, special rigs and similar devices for raising maintenance personnel to the luminaires. One known luminaire lowering system includes a luminaire ring assembly on which the luminaires are mounted and which ring assembly is mounted around a pole for movement along the vertical extent of the pole when the ring assembly is hoisted and lowered by hoisting cables attached to the assembly. The hoisting cables, typically three in number, extend from the ring assembly through a pulley system that is attached to the top of the pole and down through the interior of the pole to the base of the pole where they connect to a power winch. Electrical power is supplied to the luminaires by means of a power cable which runs from the luminaire assembly over a single pulley, down through the interior of the pole to the pole base, where it connects to the power source by way of a twistlock disconnect and circuit breaker. In the region of the disconnect, the power cable is attached to the hoisting cables such that when the luminaires are to be lowered, the power cable is disconnected from the power source so that the bulk of the power cable moves outwardly through the pole, around the power cable pulley at the top of the pole and downwardly on the outside of the pole with the lowering luminaire assembly. Problems arise during the raising and lowering operation because the elastomer-jacketed power cable tends to "walk" up over the rim of the pulley, especially when some twist exists in the cable. This occurs because the elastomer cable jacket, moving at the same tangential speed as the pulley, tends to frictionally grasp a side of the pulley groove and be carried away from the base of the pulley groove. This leads to jams in the pole top apparatus which in turn necessitates the expense of servicing and repair.
It is recognized, for proper guidance of a cable of given size through a 180.degree. turn, that the turning radius of the pulley, or other guiding means should be at least large enough to prevent internal chafing and twisting of conductors of that cable. For guidance of a power cable of the size and type typically employed with high-mount luminaires a pulley of appreciable size has been necessary. The circular profile displayed by such a pulley in a vertically extending plane at a pole top (and this includes the lower 180.degree. segment of the pulley which at any instant is not actively guiding the cable) tends to increase wind resistance and therefore adversely affect the wind performance rating of the pole.
It is an object of the invention to provide for the turning of an elastomer-jacketed power cable from one vertical path to another parallel path without the risk of jamming of the cable.
It is also an object of the invention to provide, at a high elevation pole top, for the guidance of a moving elastomer-jacketed power cable through a turn from one path to another parallel path, through a reasonable bending radius, i.e., a large enough radius to prevent internal chafing and twisting of conductors, while maintaining a minimal projected area in a vertical plane so as to reduce wind produced stress on the mounting pole.